Optimized directionless optical add/drop module systems and methods

ABSTRACT

The present disclosure provides optimized configurations for a directionless reconfigurable optical add/drop multiplexer application. The present invention includes an add module with improved optical signal-to-noise through placing amplifiers prior to a multi-cast optical switch. The present invention includes various drop module configurations utilizing distributed gain, channel selective filters, and bi-directional configurations to reduce power consumption and complexity. Additionally, the present invention includes an integrated broadcast and select architecture.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present non-provisional patent application is a continuation-in-partof U.S. patent application Ser. No. 12/268,817, filed on Nov. 11, 2008,now U.S. Pat. No. 7,899,334 and entitled “SIGNAL DISTRIBUTION MODULE FORA DIRECTIONLESS RECONFIGURABLE OPTICAL ADD/DROP MULTIPLEXER,” which is acontinuation-in-part of U.S. patent application Ser. No. 12/234,049,filed on Sep. 19, 2008, now U.S. Pat. No. 7,697,843 and entitled“MODULAR ADD/DROP MULTIPLEXER INCLUDING A WAVELENGTH SELECTIVE SWITCH,”which is a divisional of U.S. Pat. No. 7,499,652, issued on Mar. 3,2009, U.S. patent application Ser. No. 11/855,427 filed Sep. 14, 2007and entitled “MODULAR ADD/DROP MULTIPLEXER INCLUDING A WAVELENGTHSELECTIVE SWITCH,” which is a divisional of U.S. Pat. No. 7,308,197,issued on Dec. 11, 2007, U.S. patent application Ser. No. 10/768,057filed Feb. 2, 2004 and entitled “MODULAR ADD/DROP MULTIPLEXER INCLUDINGA WAVELENGTH SELECTIVE SWITCH,” which claims the benefit of priority ofU.S. Provisional Patent Application Nos. 60/444,284 and 60/443,898, bothfiled on Jan. 31, 2003, the contents of all of which are incorporated infull by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to optical communicationsystems. More specifically, the present invention relates to optimizedadd/drop modules for a directionless reconfigurable optical add/dropmultiplexer (ROADM).

BACKGROUND OF THE INVENTION

In optical communication systems, optical signals are transmitted alongan optical communication path, such as an optical fiber. Early opticalcommunication systems deployed a single optical transmitter at a nominalwavelength of light at one end of an optical fiber link and a singleoptical receiver at the other end of the optical fiber link to detectthe incoming optical signals. More recently, wavelength divisionmultiplexed (WDM) systems have been deployed in which multiplewavelengths of light are combined onto a single optical fiber in orderto increase the information carrying capacity of the opticalcommunication network.

In a WDM system, multiple optical transmitters feed optical signals toan optical multiplexer that is provided at one end of an optical fiberlink and an optical demultiplexer is provided at the other end of theoptical fiber link to separate the combined optical signal into itsconstituent optical signals at corresponding wavelengths of light.Often, however, optical communication network configurations requirethat given wavelengths of light be selected or “dropped” from thecombined optical signal prior to reaching the optical demultiplexer atthe termination point of the optical fiber link. In addition, opticalsignals at the “drop” wavelength of light or other wavelengths of lightare often required to be added prior to the termination point of theoptical fiber link. Accordingly, optical add/drop multiplexers have beendeveloped that add/drop optical signals at given wavelengths of light,while permitting optical signals at other wavelengths of light to passto the add/drop or termination points.

A conventional optical add/drop multiplexer is described, for example,in U.S. Pat. No. 6,459,516, the contents of which are incorporated infull by reference herein. This optical add/drop multiplexer flexiblyaccommodates a relatively large number of added/dropped optical signalsor channels. The channels that are added/dropped are fixed, however, andthe optical add/drop multiplexer is not remotely reconfigurable.

An alternative optical add/drop multiplexer is a select optical add/dropmultiplexer (SOADM), commercially available from CIENA Corporation ofLinthicum, Md. As illustrated in FIG. 1, the SOADM receives incomingoptical signals through an optical amplifier 110. The optical signalsare passed from the optical amplifier 110 to a power splitter or coupler120, which supplies a first portion of each incoming optical signal to areconfigurable blocking filter (RBF) 130 and a second portion of eachincoming optical signal to a pre-booster amplifier 160 and,subsequently, a router 180. The router 180 separates the second portionof each incoming optical signal into separate channel groups, one ofwhich is passed through a segment of dispersion compensating fiber (DCF)121, and then to an optical amplifier USA 197. The channel group is thenfed to a channel group demultiplexer including a 1×8 splitter 119, whichsupplies the channel group on each of eight outputs. The splitter 119 isa conventional power splitter, such that the signal strength of eachoutput is attenuated to about ⅛^(th) the power of the input. Channelfilters (not illustrated) are coupled to each output of the splitter 119to select individual channels from each output and supply thedemultiplexed channels to corresponding receivers (not illustrated).

Added channels are supplied from transmitters (not illustrated) to an8×1 combiner 117 through an amplifier 115 and a router 195. At theoutput of the router 195, the added channel group is passed through anoptional segment of DCF 190 and amplified by an amplifier 170. The addedchannel group is the combined with the channels output from the RBF 130by a coupler 140, and the resulting WDM signal is output through anamplifier 150.

In operation, the RBF 130 is configured to block the channel groupselected by a port 161 of the router 180, while the remaining channelgroups pass through. Although non-selected wavelengths of are alsosupplied to the router 180, no optical demultiplexing elements oroptical receivers are provided to sense the non-selected wavelengths oflight. The added channels are typically at the same wavelength of lightas the blocked channels in order to prevent interference between thoseoptical signals passed through the RBF 130 and those optical signalsthat are added. Alternatively, the added channels may be different fromany of the pass through channels.

Moreover, the RBF 130 may be reconfigured such that a different channelgroup is blocked. In which case, optical demultiplexers must be added toa different port or slot of the router 180, for example. Since theoptical add/drop multiplexers are often deployed in remote locations,service personnel must travel to the optical add/drop multiplexersite(s) and physically attach the channel group optical demultiplexer toa new output port of the router 180.

Alternatively, the RBF 130 may be replaced with a wavelength selectiveswitch (WSS) 210, as illustrated in FIG. 2. WSSs are known componentsthat are coupled to multiple input lines and output lines, andselectively block optical signals on a per wavelength basis. In thisinstance, the WSS 210 is coupled to input lines 209, 213, and 215, andoutput lines 222, 225, and 226. The operation of the routers and groupdemultiplexers is similar to that described above with regard to FIG. 1.However, as illustrated in FIG. 2, additional routers may be provided,each one coupled to a corresponding one of the input lines or outputlines. However, the WSS-based optical add/drop multiplexer illustratedin FIG. 2 suffers from disadvantages similar to those described abovewith regard to FIG. 1. Namely, any reconfiguration of the WSS 210resulting in a change in the wavelengths of light to be added/droppedrequires physically coupling the channel group optical demultiplexers toa different router output port.

ROADMs are the key technology for the next generation of densewavelength division multiplexing (DWDM) systems. These ROADMs allow forthe automated rearrangement of wavelengths of light on the multichanneloptical fibers entering and leaving optical network nodes. For ahigh-degree optical network node, with a degree number of up to 8, forexample, directionless ROADMs are preferred because they may route anywavelength of light on any optical fiber (or from any direction) to anygiven transceiver entirely in the optical domain.

As is described in greater detail herein below, in existing ROADMdesigns, erbium-doped fiber amplifier (EDFA) arrays with fixed gains oroutput powers are utilized in order to satisfy a worst case scenario,even though there are only M (e.g. 8 or 16) channels to be dropped for agiven modular design. This is not a cost effective solution. Each EDFAis over designed to support the worst case scenario, when all of thewavelengths of light or channels are fully populated. More than 40% ofthe associated cost is attributed to the pump lasers for the individualEDFAs. In order to simplify the design of the signal distributionmodules utilized in directionless ROADM applications, as well as shrinktheir size and lower their cost, the present invention provides a novelconfiguration that takes full advantage of type A/type B+ N×M multi-castswitches and the advanced EDFA array design with planar lightwavecircuit (PLC)-based tunable pump splitters.

BRIEF SUMMARY OF THE INVENTION

In an exemplary embodiment, an add side of a directionless opticaladd/drop module includes a multi-cast switch having a plurality of inputports and a plurality of output ports; a plurality of optical amplifiersconnected to the plurality of input ports of the multi-cast switch,wherein the plurality of optical amplifiers form an optical amplifierarray; and a plurality of tunable filters connected to the plurality ofinput ports of the multi-cast switch. Optionally, the plurality oftunable filters disposed between the plurality of input ports of themulti-cast switch and the plurality of optical amplifiers.Alternatively, the plurality of optical disposed between the pluralityof input ports of the multi-cast switch and the amplifiers plurality oftunable filters. The plurality of optical amplifiers may include aplurality of erbium-doped fiber amplifiers, and wherein the plurality oferbium-doped fiber amplifiers form an erbium-doped fiber amplifierarray. The erbium-doped fiber amplifier array may utilize a shared pumplaser.

In another exemplary embodiment, a drop side of a directionless opticaladd/drop module includes a multi-cast switch having a plurality of inputports and a plurality of output ports; a plurality of optical amplifiersconnected to the plurality of input ports of the multi-cast switch,wherein the plurality of optical amplifiers form an optical amplifierarray; and a plurality of tunable filters connected to the plurality ofoutput ports of the multi-cast switch. The plurality of opticalamplifiers may include a plurality of erbium-doped fiber amplifiers, andwherein the plurality of erbium-doped fiber amplifiers form anerbium-doped fiber amplifier array. The erbium-doped fiber amplifierarray utilizes a shared pump laser. The drop side may further includes asecond plurality of optical amplifiers connected to the plurality ofoutput ports of the multi-cast switch, wherein the second plurality ofoptical amplifiers form a second optical amplifier array, and whereinthe optical amplifier array and the second optical amplifier array areconfigured to provide distributed gain. Optionally, the second opticalamplifier array is disposed between the multi-cast switch and theplurality of tunable filters. Alternatively, the plurality of tunablefilters include a first plurality of tunable filters and a secondplurality of tunable filters, and wherein the second optical amplifierarray is disposed between the first plurality of tunable filters and thesecond plurality of tunable filters. The drop side may include a firstplurality of optical circulators connected between the optical amplifierarray and the multi-cast switch; and a second plurality of opticalcirculators connected between the first plurality of tunable filters andthe second optical amplifier array. Alternatively, the drop sideincludes a plurality of channel selective filters connected to inputs ofthe optical amplifier array. Here, the drop side may further include afirst plurality of optical circulators connected between the opticalamplifier array and the multi-cast switch; and a second plurality ofoptical circulators connected to outputs of the plurality of tunablefilters.

In yet another exemplary embodiment, an integrated directionless opticaladd/drop module includes a drop side with a broadcast and selectarchitecture; and an add side with the broadcast and selectarchitecture; wherein the broadcast and select architecture includesturning an amplifier on in a path to connect a particular transceiver toa particular degree while also turning a plurality of amplifiersconnecting the transceiver to other degrees off. The drop side and theadd side include a plurality of splitters, a plurality of combiners, aplurality of tunable filters, and a plurality of optical amplifiers. Thedrop side includes the plurality of splitters connected to the pluralityof tunable filters, the tunable filters connected to the plurality ofoptical amplifiers, the plurality of optical amplifiers connected to theplurality of combiners, and a second plurality of tunable filtersconnected to outputs of the plurality of combiners; and wherein the addside includes the plurality of splitters connected to the plurality ofoptical amplifiers, the plurality of optical amplifiers connected to theplurality of tunable filters, and the plurality of tunable filtersconnected to the plurality of combiners. The plurality of opticalamplifiers may include an amplifier array of semiconductor opticalamplifiers.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated and described herein with referenceto the various drawings of exemplary embodiments, in which likereference numbers are used to denote like system components/methodsteps, as appropriate, and in which:

FIG. 1 is a schematic diagram illustrating a conventional opticaladd/drop multiplexer design incorporating a RBF;

FIG. 2 is a schematic diagram illustrating a conventional opticaladd/drop multiplexer design incorporating a WSS;

FIG. 3 is a schematic diagram illustrating a WSS-based optical add/dropmultiplexer consistent with an aspect of the present invention;

FIGS. 4( a)-4(c) are schematic diagrams illustrating examples of tunableoptical demultiplexers consistent with an aspect of the presentinvention;

FIG. 5 is a schematic diagram illustrating a WSS-based optical add/dropmultiplexer consistent with a further aspect of the present invention;

FIG. 6 is a schematic diagram illustrating a WSS-based optical add/dropmultiplexer including a multi-cast switch consistent with a furtheraspect of the present invention;

FIGS. 7( a) and 7(b) are schematic diagrams illustrating examples ofdirectionless ROADMs consistent with an aspect of the present invention;

FIGS. 8( a) and 8(b) are schematic diagrams illustrating examples of N×Mmulti-cast switches consistent with an aspect of the present invention;

FIG. 9 is a schematic diagram illustrating a signal distribution moduleemploying an N×M multi-cast switch and a conventional EDFA arrayconsistent with an aspect of the present invention;

FIG. 10 is a schematic diagram illustrating a 4-EDFA array designutilizing 1×4 tunable splitters;

FIG. 11 is a schematic diagram illustrating a signal distribution moduleincorporating an EDFA array coupled to a shared pump laser and tunablesplitter in order to accommodate the variable insertion losses of an N×Mmulti-cast switch;

FIG. 12 is a schematic diagram illustrating an implementation for adirectionless add/drop module with a “drop” side and an “add” side;

FIGS. 13 a-13 b are schematic diagrams illustrating the add side in FIG.12 with different placements of the EDFAs;

FIGS. 14 a-14 b are schematic diagrams illustrating the drop side in thedirectionless add/drop module of FIG. 12 is illustrated with distributedgain;

FIG. 15 is a schematic diagram illustrating the drop side in thedirectionless add/drop module of FIG. 12 with channel selective filters;

FIGS. 16 a-16 b are schematic diagrams illustrating a bi-directionaldesign for the directionless add/drop module of FIG. 12; and

FIGS. 17 a-17 b are schematic diagrams illustrating an integrated designdirectionless add/drop module with a broadcast and select architecture.

DETAILED DESCRIPTION OF THE INVENTION

Consistent with the optical communication system of the presentinvention, tunable optical demultiplexers have been provided inWSS-based optical add/drop multiplexers. The tunable opticaldemultiplexers have been modular, and thus allow the optical add/dropmultiplexers to be readily expandable and facilitate flexible opticaladd/drop capabilities, whereby a channel present on any input line tothe WSS may be dropped and supplied to one or more desired output linesof the tunable optical demultiplexers. Similar flexibility has beenachieved on the add-side of the WSS. Moreover, the opticaldemultiplexers and the WSS have been remotely configurable, thusobviating the need to manually disconnect and connect the opticaldemultiplexers to a router. Multi-cast switches have been provided thatpermit the same channel, for example, to be provided to one or moreoutput lines of the optical add/drop multiplexer, such that a copy ofthe channel may carry working traffic, while another copy of the channelmay carry protection traffic. As a result, 1+1 and 1:N optical layerprotection has been achieved.

FIG. 3 illustrates a WSS-based optical add/drop multiplexer 302consistent with an aspect of the present invention. The optical add/dropmultiplexer 302 includes a WSS 315 having a plurality of input ports315-1 to 315-n each coupled to a respective one of a plurality of inputoptical communication paths 312-1 to 312-n. Each input opticalcommunication path 312-1 to 312-n may be coupled to an opticalamplifier, such as the optical amplifier 305 coupled to the first inputoptical communication path 312-1, for example. The input opticalcommunication paths 312-1 to 312-n each include commercially availableoptical fiber, for example, and the optical amplifier 305 is aconventional EDFA, for example. Input optical signals, each at aparticular wavelength of light, and collectively constituting a WDMsignal, propagate along the first input optical communication path312-1. Other WDM signals likewise propagate along the other inputoptical communication paths 312-2 to 312-n.

As further illustrated in FIG. 3, a power splitter 310-1, including, forexample, a fiber optic coupler, tap, or other suitable opticalcomponent, is coupled to the first input optical communication path312-1. Likewise, power splitters 310-2 to 310-n are coupled to the otherrespective input optical communication paths 312-2 to 312-n. A firstportion of the WDM signal propagating on the first input opticalcommunication path 312-1 is output from the power splitter 310-1,through an optional dispersion compensating module 330 and an optionaloptical amplifier 334 to an input port 332-3 of a tunable opticaldemultiplexer 332. Selected channels (i.e. optical signals at specificwavelengths of light) are respectively output from corresponding ones ofthe outputs 332-1. Other channels, however, are output through anexpansion port 332-2, and fed through an optional optical amplifier 336to an input port 338-3 of a tunable optical demultiplexer 338. Theseother channels are then separated and supplied to corresponding ones offirst outputs 338-1 and to receivers discussed in greater detail hereinbelow, but a second output 338-2 is a supplemental port not connected toany receivers.

Initially deployed WDM optical communication systems are not fullypopulated with a maximum number of channels, as capacity requirementsare typically lower at first but increase over time. Thus, a fullcomplement of optical demultiplexers may not be required at first, butrather a smaller number is sufficient to drop the relatively low numbersof channels typically present when a WDM optical communication system isfirst deployed. Accordingly, a limited number of tunable opticaldemultiplexers are often provided at system turn-up, but each has asupplemental port, not connected to receiver circuits, such thatadditional tunable optical demultiplexers may be attached later on ascapacity requirements grow. Large optical demultiplexer circuits neednot be installed early in a product life cycle. Instead, modular tunableoptical demultiplexers are added incrementally on an as-needed basis,resulting in substantial cost savings.

Returning to FIG. 3, the optical demultiplexer 332 is tunable becausethe wavelengths of light selected for output at each port may be tunedor adjusted in response to a control signal. For example, an opticalsignal having wavelength λ₁ may initially be output from one of the dropports 332-1 of the flexible optical demultiplexer 332 (i.e. the N-portdrop module). In response to a control signal, however, a differentoptical signal having wavelength λ₉ may be output.

Control information is carried by an optical service channel present onone of the input optical communication paths 312-1, for example. Anadditional optical demultiplexer 360, such as an optical filter, selectsthe optical service channel, which is typically at a wavelength of lightthat is different than the other information carrying wavelengths oflight of the WDM signal. As is generally understood, the optical servicechannel often carries optical system or optical network-relatedinformation, such as diagnostic, monitoring, as well as controlinformation. The optical service channel is output from the opticaldemultiplexer 360 and supplied to a control circuit 350, which convertsthe optical service channel into corresponding electrical signals in aknown manner, and generates appropriate control signals in response tothe received optical service channel. The control signals may besupplied to each of the tunable optical demultiplexers 332 and 338, forexample.

Adding channels is similar to dropping them, but in reverse. A pluralityof conventional tunable optical transmitters 341-1 to 341-n are coupledto respective ones of the inputs or add ports 340-1 of a combiner ortunable optical multiplexer 340. The optical multiplexer 340 also has asupplemental input or expansion port not coupled to an opticaltransmitter to accommodate further combiners as system capacityrequirements increase. Optical signals generated by the transmitters341-1 to 341-n are typically each at a different wavelength of light andare supplied to the output 340-3, through an optional optical amplifier342, and to an input or expansion port 344-2 of the combiner 344. Thecombiner 344 also receives additional optical signals, each at arespective wavelength of light, on respective ones of the add ports orinputs 344-1 from optical transmitters (not illustrated), similar to theoptical transmitters 341-1 to 341-n. The optical signals suppliedthrough the expansion port 344-2 and add ports 344-1 are combined ontothe output 344-3 and fed to the combiner 320-1, through an optionaloptical amplifier 346 and an optional dispersion compensating element348. The optical combiner 320-1 combines these optical signals withsignals output from the WSS 315 through a port 316-1 onto the outputoptical communication path 313-1, through an optional optical amplifier325. The optical amplifier 325, as well as other optical amplifiersdescribed herein, are provided to offset any attenuation of the opticalsignals passing through the WSS 315, as well as those added and droppedby the optical add/drop multiplexer 302.

Moreover, additional combiners, similar to the combiners 340 and 344,may be coupled in a similar manner to the combiners 320-2 to 320-n tofacilitate the coupling or combining of the optical signals output fromthe WSS output ports 316-2 to 316-n onto further output opticalcommunication paths 313-2 to 313-n. The tunable optical multiplexers orcombiners 340 and 344 may have a structure similar to the tunableoptical; demultiplexers 332 and 338, but are connected in reverse, suchthat the add ports input signals instead of outputting them, and theoutputs of the combiners 340 and 344 supply signals instead of receivingthem.

Although the tunable optical demultiplexers are illustrated forcombining optical signals in the various embodiments of the presentinvention, other combiners may also be utilized. For example,conventional passive optical combiners, or other suitable opticalcomponents, that combine optical signals may be used in conjunction withthe systems and methods of the present invention. It should be notedthat passive optical combiners typically cost less than tunable opticaldemultiplexers.

FIGS. 4( a)-4(c) illustrate examples of tunable optical demultiplexersconsistent with an aspect of the present invention. It should beunderstood that any of the tunable optical demultiplexers may have aconstruction as illustrated in one or more of FIGS. 4( a)-4(c). In theexample illustrated in FIG. 4( a), the tunable optical demultiplexerincludes a 1×N+1 splitter 430 having an input 425 (e.g. corresponding toan input 332-1) that receives signals supplied from the splitter 310-1(FIG. 3), for example. The splitter 430 has N+1 outputs, N of whichsupply attenuated portions of the input optical signal to correspondingtunable filters 432-1 to 432-n, each of which is controlled inaccordance with information contained in, or in response to, the opticalservice channel to select an optical signal at a desired wavelength oflight. The filtered optical signals are then supplied to correspondingreceivers 450-1 to 450-n. The N+1th output, however, corresponds to thesupplemental or expansion output to facilitate modular expansion of theoptical demultiplexing capabilities of the optical add/drop multiplexerin an inexpensive manner.

Referring to FIG. 4( b), the tunable filters 480-1 to 480-n arecascaded, whereby the optical signals fed through the input 425 arefirst supplied to the tunable filter 480-1, which reflects, for example,one of the input signals, but passes the remaining signals. Theremaining signals are then input to the tunable filter 480-2, whichselects another optical signal in a similar fashion as the tunablefilter 480-1. The remaining signals are passed from one tunable filterto the next, and, at each filter, a different channel is selected. Theselected channels are, in turn, fed to corresponding receivers 450-1 to450-n. If any channels are not selected by the tunable filters 480-1 to480-n, they are fed to a supplemental output 452 for propagation toanother tunable optical demultiplexer, as noted above. The tunablefilters 480-1 to 480-n are controlled in response to the optical servicechannel.

As illustrated in FIG. 4, an integrated N-port drop module includingtunable filters configured as illustrated in either FIG. 4( a) or FIG.4( b) may also be provided. In which cases, the tunable filters andother necessary components are integrated into a single componenthousing 490. As in other examples, a supplemental port 452 is alsoincluded.

The tunable filters illustrated above are commercially available fromJDS Uniphase, Optoplex, or Dicon, for example. The integrated N-portdrop module illustrated in FIG. 4( c) is also commercially availablefrom JDS Uniphase, for example.

As noted previously, the exemplary embodiment illustrated in FIG. 3provides a cost effective, yet flexible, approach to expanding aWSS-based optical add/drop multiplexer. An alternative exemplaryembodiment will next be described with reference to FIG. 5 illustratingan optical add/drop multiplexer 510 consistent with a further aspect ofthe present invention.

As with the optical add/drop multiplexer 302 illustrated in FIG. 3, theexemplary embodiment illustrated in FIG. 5 also includes a WSS 315, aswell as a plurality of input and output optical communication paths andsplitters 310-1 to 310-n. In addition, the optical add/drop multiplexer510 illustrated in FIG. 5 similarly includes combiners 320-1 to 320-nand output optical communication paths, as discussed above in regard toFIG. 3. The operation of these elements is as before.

The optical add/drop multiplexer 510, however, differs from the opticaladd/drop multiplexer 302 described previously in that the tunableoptical demultiplexers and multiplexers with supplemental or expansionports are replaced with an additional splitter 520 and combiner 534, forexample. Tunable demultiplexers 526 and 528 are also typically included.Although each of the tunable elements 526, 528, 530 and 532 areillustrated without supplemental ports, such supplemental ports may beprovided, if necessary, and further tunable optical demultiplexers andmultiplexers may attached in a manner similar to that described above inregard to FIG. 3.

The operation of optical add/drop multiplexer 510 will next bedescribed. Optical signals input from the splitter 310-1 and dispersioncompensation element 330, for example, are supplied to an opticalsplitter 520, typically a power splitter, through an input 520-1 which,in turn, supplies portions of the received optical signals to each ofthe outputs 520-2 to 520-4. The outputs 520-2 and 520-4 are respectivelycoupled, through optical amplifiers 522 and 524, to tunable opticaldemultiplexers 526 and 528, which separate the optical signals inputthereto in response to the optical service channel carried on an inputoptical communication path, for example, in a manner similar to thatdescribed above with respect to FIGS. 3 and 4( a)-4(c). As a result,desired dropped channels are output from the drop ports illustrated inFIG. 5. It should be understood that additional splitters are coupled tothe splitters 310-2 to 310-n, and additional tunable opticaldemultiplexers are coupled to these additional splitters in a mannersimilar to that discussed above in regard to the splitter 520 andtunable optical demultiplexers 526 and 528.

The optical splitter 520 also has a supplemental port or output 520-3not coupled to a tunable optical demultiplexer. The supplemental output520-3 may accommodate an additional tunable optical demultiplexer,should one be needed in light of increased capacity needs requiring thatadditional channels be dropped. Upon initial deployment, however, whenan optical communication system is not fully populated with WDM signals,as noted above, the supplemental output 520-3 of the splitter 520, forexample, allows for modular expansion and a cost-effective upgrade path.

As further illustrated in FIG. 5, added channels are supplied to thetunable optical multiplexers or combiners 530 and 532 in a mannersimilar to that described above with respect to the tunable opticalmultiplexers 340 and 344. In response to the optical service channel,the tunable optical multiplexers 530 and 532 combine signals suppliedthereto typically onto a single output, which is coupled tocorresponding inputs 534-1 and 534-3 or the combiner 534. The signalsoutput from the tunable optical multiplexers 530 and 532 are thenfurther combined onto an output 534-4 of the combiner 534. These signalsare then optionally amplified by an amplifier 536, passed thoughoptional dispersion compensating element 538, and fed to an outputoptical communication path by a combiner 320-1.

The combiner 534 has a supplemental input not coupled to a tunableoptical multiplexer, for expansion purposes and accommodating modulargrowth.

Further combiners, similar to the combiner 534, are also coupled tocorresponding ones of the combiners 320-2 to 320-n. Also, an additionaltunable optical multiplexer may be coupled to such further combiners ina similar fashion as that described above in regard to the tunableoptical multiplexers 530 and 532.

The optical add/drop multiplexers discussed above are advantageous inthat each may provide a cost-effective growth path for system operatorsand users. Moreover, these optical add/drop multiplexers providesubstantial flexibility by permitting the dropping of any channelpresent on a particular input optical communication path. Further, anychannel may be added to a particular output optical communication path.Nevertheless, the above-described exemplary embodiments are limited inthat each tunable optical demultiplexer and multiplexer is dedicatedeither to a particular input or output optical communication path.Greater system flexibility may be achieved when the tunable opticaldemultiplexers and multiplexers may be coupled to any input or outputoptical communication path of the WSS, as discussed in greater detailbelow with respect to FIG. 6.

The optical add/drop multiplexer 610 illustrated in FIG. 6 is similar tothe optical add/drop multiplexer 510 illustrated in FIG. 5. Instead ofproviding splitters, such as the splitter 520, however, being coupled toa bank of optical amplifiers and tunable optical demultiplexers, aplurality of splitters 612-1 to 612-n are provided, each of which iscoupled to a corresponding one of the splitters 310-1 to 310-n. Each ofthe splitters 612-1 to 612-n typically has an output coupled, through arespective one of the amplifiers 618-1 to 618-n, to a multi-cast opticalswitch 624 (such as an 8×8 multi-cast optical switch commerciallyavailable from Lynx PhotoniNEL or Enablence, for example). On the addside, a multi-cast optical switch 634 is provided for coupling tunableoptical multiplexers to desired output optical communication paths.

In operation, a portion of the WDM signal present on input opticalcommunication path 312 is passed through an optional dispersioncompensating element 330-1 and supplied to a splitter 612-1. Thesplitter 612-1 typically includes a plurality of outputs, one of whichsupplies a further portion of the optical signals to the multi-castswitch input 624-1 via an amplifier 618-1. The multi-cast optical switch624 (illustrated as an M×M optical switch, where M is an integer, e.g.8) acts to further power split the signal input thereto, but suppliesthe split signals to selected outputs, instead of all of its outputs (asin the case of a conventional 1×N splitter.) Thus, for example, signalsappearing on the input 624-1 may be supplied to the output 624-5 andother selected outputs, but not every output. In which case, since theoutput 624-5 is coupled to the tunable optical demultiplexer 626,optical signals originating on the input optical communication path312-1 are only supplied to the tunable optical demultiplexer 626, aswell as other selected tunable optical demultiplexers, for example, thetunable demultiplexer 628 through the output 624-7. If desired, alltunable optical demultiplexers are coupled to the multi-cast opticalswitch 624. Receiver circuits 696-1 to 696-n may be coupled to therespective ports or outputs of the tunable optical demultiplexer 626.Similar receiver circuits are coupled to the drop ports or outputs oftunable optical demultiplexer 628, as well as any other tunable opticaldemultiplexer coupled to the multi-cast switch 624.

As further illustrated in FIG. 6, other input optical communicationpaths 312-2 to 312-n are respectively coupled to the multi-cast switchinputs 624-2 to 624-n via corresponding ones of the splitters 312-2 to312-n, optional dispersion compensating elements 330-2 to 330-n, andoptional amplifiers 618-2 to 618-n. Accordingly, the multi-cast switch624 may serve to couple any input optical communication path to anytunable optical demultiplexer.

The multi-cast optical switches and tunable optical demultiplexers andmultiplexers illustrated in FIG. 6 are controlled in response to anoptical service channel present on the input optical communication path312-1, for example. As noted above, the demultiplexer 360 selects theoptical service channel from the input optical communication path 360and supplies the optical service channel to the control circuit 350. Theoptical service channel is converted to electrical signals by thecontrol circuit 350 and control signals are generated that are used tocontrol the tunable elements 624, 626, 628, 630, 632, and 634, forexample.

As further illustrated in FIG. 6, the multi-cast optical switch 634 maybe used to couple any add port to any WSS output optical communicationpath. For example, optical signals supplied to the add ports from thetunable transmitters 697-1 to 697-n (it should be understood thatsimilar transmitters are coupled to the add ports of the tunable opticalmultiplexer 632, as well as any other tunable optical multiplexercoupled to the multi-cast optical switch 634) or inputs of the tunableoptical multiplexer or combiner 630 are combined and supplied to theinput 634-1 of the multi-cast optical switch 634. If desired, themulti-cast optical switch 634 may direct those optical signals to aparticular output, e.g. the output 634-6. From there, the opticalsignals pass through the splitter 690-6, optional optical amplifier640-2, and dispersion compensating element 638-2. The optical signalsare next combined with the output signals from the WSS 315 onto theoutput optical communication path 313-2 by the combiner 320-2.Alternatively, these optical signals could be supplied to other outputoptical communication paths through one or more other outputs 634-5 to634-n of the multi-cast optical switch 634, and corresponding ones ofthe splitters 690-5 to 690-n, optional optical amplifiers 640-1 to640-n, dispersion compensating elements 638-1 to 638-n, and combiners320-1 to 320-n. In a similar fashion, the multi-cast optical switch 634may couple other tunable optical multiplexers or combiners, such as thetunable optical multiplexer 632, to any one of the output opticalcommunication paths 313-1 to 313-n, or be combined with the output fromthe tunable optical multiplexer 630 and supplied to any desired outputoptical communication path.

In accordance with a further aspect of the present invention, thesplitter 612-1 may be provided with a supplemental output or expansionport 612-20 not connected to the multi-cast switch 624, but for couplingto an additional multi-cast optical switch, if necessary. Moreover, themulti-cast optical switches 624 and 634 may also include a supplementaloutput 624-6 and supplemental input 634-2, respectively, also forexpansion purposes. Further, the combiner 690-5 includes a supplementalinput 604 not coupled to the multi-cast switch 634, but included forcoupling to additional multi-cast optical switches, as dictated bysystem and capacity requirements.

The optical add/drop multiplexer illustrated in FIG. 6 advantageouslymay provide 1+1 protection. For example, the input optical communicationpath 312-1 may serve as a working path, while input the input opticalcommunication path 312-2 may serve as a protection path. During normaloperation, information carried by the working path 312-1 may be directedby the multi-cast switch 624 toward the receiver circuit 696-1. Inresponse to a fault on the working path 312-1, the multi-cast switch 624(which can also constitute an L×M switch, where L and M do notnecessarily have the same value) may route signals originating from theinput optical path 312-2, the protection path, to the output 624-5 andto the tunable demultiplexer 626, which itself may be controlled toselect the desired optical signals. Such rerouting may be achieved inless than 2 msec, thereby effectively realizing a 1+1 protection scheme.

Protection schemes may also be realized on the add side. For example,the optical signals originating from the tunable optical transmitter697-1 may be directed toward a working output optical communication path313-1 by the multi-cast switch 634 through the output 634-5 to thecombiner 690-5, optional dispersion compensating element 638-1, optionaloptical amplifier 640-1, and combiner 320-1. In response to a fault onthe optical communication path 313-1, optical signals from transmitter697-1 may be rerouted by the multi-cast optical witch 634 to be suppliedthrough the output 634-6 to the output optical communication path (aprotection path) via the combiner 690-6, optional amplifier 640-2,optional dispersion compensating element 638-2, and combiner 320-2. Byfacilitating the use of both working and protection paths, 1+1 and 1:Nprotection schemes may be achieved.

Again, ROADMs are the key technology for the next generation of DWDMsystems. These ROADMs allow for the automated rearrangement ofwavelengths of light on the multichannel optical fibers entering andleaving optical network nodes. For a high-degree optical network node,with a degree number of up to 8, for example, directionless ROADMs arepreferred because they may route any wavelength of light on any opticalfiber (or from any direction) to any given transceiver entirely in theoptical domain.

Several architectures have been proposed for directionless ROADMs,including the incorporation of a power splitter followed by a receiverwith a tunable selector, which is one of the more promising designs thatsupports full-flexibility directionless add/drop in a modular approach.This architecture is described in U.S. Pat. No. 7,308,197, the contentsof which are incorporated in full by reference herein which is based onN×M multi-cast switches 710 and 720, as is illustrated in FIGS. 7( a)and 7(b).

Referring to FIGS. 7( a) and 7(b), the key enabler for this architectureis to have a directionless signal distribution module that is powered byits N×M multi-cast switches 710 and 720 for dynamic optical signalrerouting without wavelength or direction constraints. This signaldistribution module has N inputs 711-1 to 711-n from N ports 713-1 to713-n and M outputs 712-1 to 712-m and a tunable receiver 714 equippedwith a tunable filter (not illustrated) that is utilized to select theexact wavelength for drop (see FIG. 7( a)) A similar design isimplemented at the add side (see FIG. 7( b)), with a tunable transmitter724 equipped with a tunable filter (not illustrated) that is utilized toselect the exact wavelength for add and M inputs 721-1 to 721-m and Noutputs 722-1 to 722-n to N ports 723-1 to 723-n.

In general, there are two types of N×M multi-cast switches. Type A isrealized through PLC technology by cascading 2×2 thermo-opticMach-Zehnder switches 810 in an N×M configuration (see FIG. 8( a)),which has been disclosed by Infineon and Lynx Photonics in 2000 and2001, for example. In this configuration, signals experience differentinsertion losses (ILs) under different splitting conditions, where extravariable optical attenuator (VOA) stages are normally built in at theoutput side to balance the output optical power per channel (or perwavelength). Other PLC vendors, such as NEL, for example, can build thistype of N×M multi-cast switches by modifying their current N×N opticalswitch matrices. Type BN×M multi-cast switches are achieved byconnecting discrete N1×M splitter arrays 820 and MN×1 switch arrays 822,as illustrated in FIG. 8( b). The MN×1 switch arrays 822 may be based onany technology, including three-dimensional (3D) micro-electromechanicalsystem (MEMS) technology. In most designs, type BN×M multi-cast switchesutilize a fixed splitter at the front end, such that all of the opticalpaths have the same ILs. Advanced technologies may be utilized tomanufacture tunable splitters as well, and manufacture type BN×Mmulti-cast switches having similar functions as type AN×M multi-castswitches, such as type B+ N×M multi-cast switches. Enablence is a vendorof such components, for example.

Referring to FIG. 9, the ILs introduced by optical power splittingthrough either a fixed power splitting ratio in type BN×M multi-castswitches or a reconfigurable power splitting ratio in type A or type B+multi-cast switches may be compensated for utilizing EDFAs 920-1, 920-2,and 920-n arranged in an array and coupled to the N×M multi-cast switch910.

Type B multi-cast switches with fixed power splitting ratios have fixedILs for all of the associated optical communication paths that arerelatively easy to manage with a conventional EDFA array, which isnormally running in a constant gain or constant power mode. In order toensure the per channel optical power output of the N×M multi-cast switch910 meeting certain power level specifications, each EDFA 920-1, 920-2,and 920-n of the EDFA array should be powerful enough to cover the largeILs of the type BN×M multi-cast switch. It will be readily apparent tothose of ordinary skill in the art that type A multi-cast switches mayalso be used in this design, but the IL for each optical communicationpath varies from configuration to configuration, unless VOAs are used tobalance this power variation.

On the other hand, silica-based PLCs have been implemented in EDFAdesign for several years because of their superior stability, highreliability, and impressive flexibility. Recently, JDS Uniphase hasbuilt a three-stage erbium amplifier prototype using a PLC chip thatincludes 980 nm/1550 nm WDMs, fixed ratio taps, variable opticalattenuators, and a 980 nm pump laser/tunable splitter. The use of atunable splitter allowed the pump laser to be operated more efficientlyand inexpensively. This type of design does not provide significant costadvantages for a single EDFA, but it is feasible to build smaller sizeand lower cost EDFA arrays (see, e.g. U.S. Pat. No. 6,980,576).

FIG. 10 is a schematic diagram illustrating a design utilizing fourEDFAs 1010 arranged in an array 1020 and using 1×4 tunable splitters1030. The EDFA array 1020 may share up to four pumps 1040, for example,to maximize the output power. The 1×4 tunable splitters may beintegrated with other components, such as VOAs and 980 nm/1550 nm WDMs,for example. This concept may be extended to an array of eight EDFAs,etc.

Again, in existing ROADM designs, EDFA arrays with fixed gains or outputpowers are utilized in order to satisfy a worst case scenario, eventhough there are only M (e.g. 8 or 16) channels to be dropped for agiven modular design. This is not a cost effective solution. Each EDFAis over designed to support the worst case scenario, when all of thewavelengths of light or channels are fully populated. More than 40% ofthe associated cost is attributed to the pump lasers for the individualEDFAs. In order to simplify the design of the signal distributionmodules utilized in directionless ROADM applications, as well as shrinktheir size and lower their cost, the present invention provides a novelconfiguration that takes full advantage of type A/type B+ N×M multi-castswitches and the advanced EDFA array design with PLC-based tunable pumpsplitters.

Referring to FIG. 11, signal distribution module 1100 of the presentinvention includes an EDFA array 1110 incorporating N EDFAs 1110-1,1110-2, 1110-3, and 1110-n coupled to N inputs 1112-1, 1112-2, 1112-3,and 1112-n of an N×M multi-cast switch 1120 including M outputs 1122-1to 1122-m, as well as to a shared pump laser 1130 and a 1×N tunablesplitter, in order to accommodate the variable ILs of the N×M multi-castswitch 1120. For example, as illustrated in FIG. 11, a 4×8 multi-castswitch 1120 is configured as a 1×4 splitter for input port 1 1112-1(with 6 dB theoretical splitting loss) and a 1×3 splitter for input port2 1112-2 (with 5 dB theoretical splitting loss), with no connection forinput port 3 1112-3 and a one-to-one connection for input port 4 1112-n(with 0 dB theoretical splitting loss). In this configuration, differentamounts of the pump laser signal may be delivered to each EDFA 1110-1,1110-2, 1110-3, and 1110-n—50% to EDFA 1 1110-1, 40% to EDFA 2 1110-2,none to EDFA 3 1110-3, and 10% to EDFA 4 1110-n. Thus, the following maybe achieved: 6 dBm total output power from EDFA 1 1110-1, 5 dBm totaloutput power from EDFA 2 1110-2, no light from EDFA 3 1110-3, and 0 dBmtotal output power from EDFA 4 1110-n. After the 4×8 multi-cast switch1130, an equal power of −3 dBm is observed at all the output ports1122-1 to 1122-m (assuming a 3 dB intrinsic IL for each of theswitches).

The signal distribution module of the present invention represents anideal solution for directionless ROADM applications as it represents alow cost, compact, low power consumption assembly. For example, up to an8-channel drop may be realized on a single one-slot card.

Referring to FIG. 12, in an exemplary embodiment, a typicalimplementation for a directionless add/drop module 1200 as describedherein includes a “drop” side 1202 and an “add” side 1204 with threemajor parts: EDFAs 1206, N×M multi-cast switches 1208, and tunablefilters 1210. At the “drop” side 1202, the 4×8 multi-cast switches 1208are used to deliver the function of all directing wavelengths from anydirection to any transceiver, where the tunable filter 1210 at eachoutput of multi-cast switches 1208 is used to select the specificwavelength channel to the receiver. The EDFAs 1206 are needed tocompensate the insertion loss (IL) of multi-cast switches 1208 andtunable filters 1210. Similarly, at the “add” side 1204, the 4×8multi-cast switches 1208 are used to combine the output signal from anytransmitter at any wavelength to specific direction, where the tunablefilter 1210 at the input of the multi-cast switches 1208 is used tolimit the bandwidth of high speed signals and to suppress out-of-bandASE. Again, the EDFAs 1206 are used to compensate the insertion loss ofmulti-cast switches 1208 and tunable filters 1210.

At the drop side 1202, in order to support only eight-channel drop, thefour EDFAs 1206 in the typical implementation have to achieve very highoutput powers considering the amplification of all WDM channels, makingthis design extreme low efficiency in term of EDFA usage. U.S. patentapplication Ser. No. 12/268,817, filed on Nov. 11, 2008, and entitled“SIGNAL DISTRIBUTION MODULE FOR A DIRECTIONLESS RECONFIGURABLE OPTICALADD/DROP MULTIPLEXER” (the parent case of this application), proposes anovel pump-sharing solution to reduce the total pump power requirements.However, this scheme requires fast transient control. Secondly, sincethere will be a large scale combiner (e.g., 1×12 combiner) in typical“add” design to combine all the signals from each directionless add/dropmodule, the accumulation of amplified stimulated emission (ASE) which isgenerated by those “add” EDFAs 1206 could result in large opticalsignal-to-noise ratio (OSNR) penalties, particularly when those EDFAs1206 are running at high gain with low input powers. Additionally, theEDFAs 1206 will require transient control if they are implemented at theoutput side of multi-cast switches 1208, making it difficult to do pumpsharing.

Referring to FIGS. 13 a-13 b, in an exemplary embodiment, the add side1204 in the directionless add/drop module 1200 of FIG. 12 is illustratedwith different placements of the EDFAs 1206. Specifically, FIG. 13 aillustrates placement of the EDFAs 1206 prior to the tunable filters1210, and FIG. 13 b illustrates placement of the EDFAs 1206 between thetunable filters 1210 and the multicast switch 1208. Note, in FIG. 12,the add side 1204 includes the EDFAs 1206 after the multicast switch.Advantageously, the exemplary embodiments in FIGS. 13 a-13 b includeimproved the OSNR at the add side 1204 and reduced complexity of pumplaser control (associated with the EDFAs 1206). Though it requires fourmore sets of EDFA passive components, it could improve the OSNR by morethan 10 dB and require just one shared pump laser among the EDFAs 1206.

Referring to FIGS. 14 a-14 b, in an exemplary embodiment, the drop side1202 in the directionless add/drop module 1200 of FIG. 12 is illustratedwith distributed gain. Advantageously, the exemplary embodiments ofFIGS. 14 a-14 b cut the number of pump lasers and reduce total powerconsumption at the drop side 1202 utilizing distributed gain. Thedistributed gain is achieved using two-stages of EDFAs 1410, 1420 atboth the input and output side of multi-cast switches 1208. The secondstage EDFAs can be put after the tunable filters 1210 as illustrated inFIG. 14 a, or between a mid-stage of tunable filters 1430, 1440 asillustrated in FIG. 14 b. Clearly, these second stage 8-channel EDFA1410, 1420 arrays have no transient control requirements and can share asmall pump laser. Though it may require more EDFA passive components, itsignificantly reduces the output power requirements for the first stageEDFAs 1410, and effectively reduces the total power consumption andcost.

Referring to FIG. 15, in an exemplary embodiment, the drop side 1202 inthe directionless add/drop module 1200 of FIG. 12 is illustrated withchannel selective filters 1510. The channel selective filters 1510 maybe a reconfigurable blocking filter (RBF), also known as wavelengthblocker, or the like. Here, the channel selective filters 1510 filterout unneeded wavelengths thereby reducing the associated powerconsumption of the EDFAs 1206. Specifically, with only up to eightchannels to be amplified for each “drop” EDFA 1206, pump powerrequirements are reduced dramatically, i.e. the channel selectivefilters 1510 block all but eight channels.

Referring to FIGS. 16 a-16 b, in an exemplary embodiment, abi-directional design 1600 is illustrated for the directionless add/dropmodule 1200 of FIG. 12. FIGS. 16 a-16 b illustrate the bi-directionaldesign 1600 with respect to the drop side 1202 in the directionlessadd/drop module 1200 of FIG. 12. FIG. 16 a illustrates the embodiment ofFIG. 14 b utilizing the bi-directional design 1600 for “drop” withdistributed gain. FIG. 16 b illustrates the embodiment of FIG. 15 withthe bi-directional design 1600 for “drop” with channel selective filters1510. To achieve the bi-directional design 1600, a pair of circulators1610, 1620 is on either side of the multi-cast switch 1208. In FIG. 16a, the circulators 1610 are disposed between the EDFAs 1410 and themulti-cast switch 1208 and the circulators 1620 are disposed between thefirst set of tunable filters 1430 and the EDFAs 1420. In FIG. 16 b, thecirculators 1610 are disposed between the EDFAs 1206 and the multi-castswitch 1208, and the circulators 1620 are disposed between the tunablefilters 1210 and drop/add ports.

Referring to FIGS. 17 a-17 b, in an exemplary embodiment, an integrateddesign directionless add/drop module 1700 is illustrated with abroadcast and select architecture. Specifically, FIG. 17 a illustratesan integrated drop side 1702 and FIG. 17 b illustrates an integrated addside 1704. Advantageously, the integrated design directionless add/dropmodule 1700 provides smaller size and power consumption than the otherembodiments described herein. In this approach, the multicast switch1208 is replaced is replaced by amplifier arrays 1710, splitters 1720,and combiners 1730. In FIG. 17 a, the drop side 1702 includes splitters1720 receiving input signals of a plurality of wavelengths. Thesplitters 1720 split out specific wavelengths that are then filtered toa single wavelength or group of wavelengths through the tunable filters1740. The amplifier array 1710 is configured to amplify the output ofeach of the tunable filters 1740. The amplifier array 1710 may includesemiconductor optical amplifiers (SOAs) or the like. Outputs from eachof the splitters 1720 are connected to each of the combiners 1730through the intermediate tunable filters 1740 and the amplifier array1710. The combiners 1730 combine each of the inputs and include tunablefilters 1750 on the output to filter or select a desired wavelength. Inthe integrated design directionless add/drop module 1700, to connect aparticular transceiver to a particular degree, the amplifier 1710 in thepath between the degree input/output and the transceiver is turned on,while the amplifiers 1710 connecting the transceiver to other degreesare turned off. In FIG. 17 b, the add side 1704 includes splitters 1720receiving an input signal and splits the input to each of the amplifiersin the amplifier array 1710. The amplifier array 1710 connects to thetunable filters 1740 which in turn connect to the combiners 1730 whichcombine the outputs of the tunable filters 1740.

Although the present invention has been illustrated and described hereinwith reference to preferred embodiments and specific examples thereof,it will be readily apparent to those of ordinary skill in the art thatother embodiments and examples may perform similar functions and/orachieve like results. All such equivalent embodiments and examples arewithin the spirit and scope of the present invention, are contemplatedthereby, and are intended to be covered by the following claims.

What is claimed is:
 1. An add side of a directionless optical add/dropmodule, comprising: a multi-cast switch having a plurality of inputports and a plurality of output ports; a plurality of optical amplifiersconnected to the plurality of input ports of the multi-cast switch,wherein the plurality of optical amplifiers form an optical amplifierarray; and a plurality of tunable filters connected to the plurality ofinput ports of the multi-cast switch; wherein the add side utilizes abroadcast and select architecture comprising enabling an amplifier in apath to connect a particular transceiver to a particular degree whilealso disabling a plurality of amplifiers connecting the transceiver toother degrees.
 2. The add side of claim 1, wherein the plurality oftunable filters disposed between the plurality of input ports of themulti-cast switch and the plurality of optical amplifiers.
 3. The addside of claim 1, wherein the plurality of optical disposed between theplurality of input ports of the multi-cast switch and the amplifiersplurality of tunable filters.
 4. The add side of claim 1, wherein theplurality of optical amplifiers comprise a plurality of erbium-dopedfiber amplifiers, and wherein the plurality of erbium-doped fiberamplifiers form an erbium-doped fiber amplifier array.
 5. The add sideof claim 4, wherein the erbium-doped fiber amplifier array utilizes ashared pump laser.
 6. A drop side of a directionless optical add/dropmodule, comprising: a multi-cast switch having a plurality of inputports and a plurality of output ports; a plurality of optical amplifiersconnected to the plurality of input ports of the multi-cast switch,wherein the plurality of optical amplifiers form an optical amplifierarray; and a plurality of tunable filters connected to the plurality ofoutput ports of the multi-cast switch; wherein the drop side utilizes abroadcast and select architecture comprising enabling an amplifier in apath to connect a particular transceiver to a particular degree whilealso disabling a plurality of amplifiers connecting the transceiver toother degrees.
 7. The drop side of claim 6, wherein the plurality ofoptical amplifiers comprises a plurality of erbium-doped fiberamplifiers, and wherein the plurality of erbium-doped fiber amplifiersforms an erbium-doped fiber amplifier array.
 8. The add side of claim 7,wherein the erbium-doped fiber amplifier array utilizes a shared pumplaser.
 9. The drop side of claim 6, further comprising: a secondplurality of optical amplifiers connected to the plurality of outputports of the multi-cast switch, wherein the second plurality of opticalamplifiers form a second optical amplifier array, and wherein theoptical amplifier array and the second optical amplifier array areconfigured to provide distributed gain.
 10. The drop side of claim 9,wherein the second optical amplifier array is disposed between themulti-cast switch and the plurality of tunable filters.
 11. The dropside of claim 9, wherein the plurality of tunable filters comprise afirst plurality of tunable filters and a second plurality of tunablefilters, and wherein the second optical amplifier array is disposedbetween the first plurality of tunable filters and the second pluralityof tunable filters.
 12. The drop side of claim 11, further comprising: afirst plurality of optical circulators connected between the opticalamplifier array and the multi-cast switch; and a second plurality ofoptical circulators connected between the first plurality of tunablefilters and the second optical amplifier array.
 13. The drop side ofclaim 6, further comprising: a plurality of channel selective filtersconnected to inputs of the optical amplifier array.
 14. The drop side ofclaim 13, further comprising: a first plurality of optical circulatorsconnected between the optical amplifier array and the multi-cast switch;and a second plurality of optical circulators connected to outputs ofthe plurality of tunable filters.
 15. An integrated directionlessoptical add/drop module, comprising: a drop side comprising a broadcastand select architecture; and an add side comprising the broadcast andselect architecture; wherein the broadcast and select architecturecomprises turning an amplifier on in a path to connect a particulartransceiver to a particular degree while also turning a plurality ofamplifiers connecting the transceiver to other degrees off.
 16. Theintegrated directionless optical add/drop module of claim 15, whereinthe drop side and the add side comprise a plurality of splitters, aplurality of combiners, a plurality of tunable filters, and a pluralityof optical amplifiers.
 17. The integrated directionless optical add/dropmodule of claim 16, wherein the drop side comprises the plurality ofsplitters connected to the plurality of tunable filters, the tunablefilters connected to the plurality of optical amplifiers, the pluralityof optical amplifiers connected to the plurality of combiners, and asecond plurality of tunable filters connected to outputs of theplurality of combiners; and wherein the add side comprises the pluralityof splitters connected to the plurality of optical amplifiers, theplurality of optical amplifiers connected to the plurality of tunablefilters, and the plurality of tunable filters connected to the pluralityof combiners.
 18. The integrated directionless optical add/drop moduleof claim 16, wherein the plurality of optical amplifiers comprise anamplifier array of semiconductor optical amplifiers.